MYOCARDIAL BLOOD FLOW IN REVERSIBLE CHRONIC LEFT VENTRICULAR DYSFUNCTION Background: Whether myocardial blood flow (MBF) is reduced or normal in reversible chronic LV dysfunction remains controversial. In this study, we determined the prevalence of reduced MBF in asynergic myocardial regions that improve function after revascularization (revasc). Methods: To this end, 35 pts with chronic CAD and LV dysfunction (LVEF=31+8%) underwent pre-revasc 13N-ammonia or 15O-water and 18F-deoxyglucose (FDG) PET at rest, and stress-redistribution-reinjection thallium SPECT. Pre- and post-revasc regional function were assessed by gated cardiac MRI or radionuclide angiography. MBF was considered to be reduced if it was 1SD below the mean MBF of regions with normal resting function and normal stress thallium; that is <0.48ml/min/g. Results:Among 132 asynergic regions that were revascularized, 72(55%) improved and 60 did not improve post-revasc. Of the 72 asynergic regions that improved post-revasc, 15(21%) had MBF<0.48 and 57 had MBF>0.48, whereas among the 60 asynergic regions that did not improve post-revasc, 19(32%) had MBF<0.48 and 41 had MBF>48 (p=NS). Among regions with MBF<0.48, 44% showed recovery of function post-revasc. These regions had higher FDG, late 13N-ammonia, and thallium uptake compared to hypoperfused regions that did not improve post-revasc. Conclusions: These findings indicate that MBF in reversible chronic LV dysfunction is heterogeneous,as 21% of asynergic regions that show functional recovery post-revasc exhibit reduced MBF at rest.